Lubricants

19 pages, 3556 KB

Open AccessArticle

Analysis and Optimization of Thermoelastohydrodynamic Lubrication Characteristics of Tooth Surfaces with Different Micro-Texture Configurations

by Jie Tang, Rongxue Huang, Sheng Huang, Yujie Qin and Hao Fan

Lubricants 2026, 14(4), 159; https://doi.org/10.3390/lubricants14040159 - 6 Apr 2026

Abstract

With the changing demands of society, gears, as fundamental components of mechanical devices, are evolving towards higher reliability and longer service life. To address the issue of thermal scuffing at the gear meshing interface, we propose the introduction of micro/nano-textures to improve the [...] Read more.

With the changing demands of society, gears, as fundamental components of mechanical devices, are evolving towards higher reliability and longer service life. To address the issue of thermal scuffing at the gear meshing interface, we propose the introduction of micro/nano-textures to improve the thermal elastohydrodynamic lubrication characteristics of the meshing surfaces, thereby enhancing the lubrication performance and anti-scuffing load capacity of the gear surfaces. First, finite element models with different microstructural features were established. Then, numerical calculations were conducted using computational fluid dynamics (CFD) software to analyze the impact of various micro-texture configurations on the lubrication performance of the tooth surface. Finally, an orthogonal experiment was performed to optimize the groove length, groove width, and areal density of the micro-textures in order to obtain the best processing parameters. The results show that, compared with the triangular, rectangular and trapezoidal micro-textures, the wedge-shaped micro-texture produces the largest pressure difference at the meshing-in and meshing-out points of the texture grooves, which causes the dynamic pressure effect to be more obvious. Compared with the triangular, rectangular and trapezoidal micro-textures, the wedge-shaped micro-texture has the largest bearing capacity and the smallest friction coefficient, so it has better bearing capacity and anti-friction and wear performance. The process parameters were optimized through orthogonal experiments, and the optimal combination of process parameters was obtained as the areal density of 50%, the depth of micro-pits of 12 µm, and the width of micro-pits of 200 µm. Under these optimal parameters, the pressure difference at the meshing-in and meshing-out points of the wedge micro-texture increased significantly by 255.6% compared to the initial model, and the oil film friction coefficient decreased by 17.857% relative to the initial model. These results demonstrate that the micro-texture with optimal parameters significantly enhances the lubrication and anti-friction/wear performance of the tooth surface. Full article

(This article belongs to the Special Issue Advanced Gear Tribology)

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14 pages, 2396 KB

Open AccessArticle

Vacuum Modification of the Surface Properties of T15K6 Hard Alloy by Plasma–Chemical Synthesis of TiN-Cu Coatings

by Aleksandr Semenov, Dmitriy Tsyrenov, Nikolay Ulakhanov, Irina Semenova, Undrakh Mishigdorzhiyn, Wen Ma, Simon C. Tung and George E. Totten

Lubricants 2026, 14(4), 158; https://doi.org/10.3390/lubricants14040158 - 6 Apr 2026

Abstract

The design and main parameters of a plasma–chemical reactor containing two compartments are presented. One compartment houses a vacuum-arc evaporator, while the other houses a planar magnetron. The compartments are separated by a diaphragm with a dosing slot for injecting copper vapor into [...] Read more.

The design and main parameters of a plasma–chemical reactor containing two compartments are presented. One compartment houses a vacuum-arc evaporator, while the other houses a planar magnetron. The compartments are separated by a diaphragm with a dosing slot for injecting copper vapor into the TiN synthesis compartment. The conditions for the synthesis of superhard TiN-Cu composite coatings are experimentally determined. Based on established process parameters for TiN synthesis in a nitrogen-containing plasma by Ti evaporation using a vacuum-arc discharge, it is proposed to apply TiN-Cu coatings by injecting Cu vapor into the TiN synthesis area and sputtering Cu using a magnetron discharge. XRD analyses of both TiN and TiN-Cu coatings show the presence of WC, Ti₂C, and TiN. EDS analysis confirms 5.57 at. % copper on the surface of the TiN-Cu coating. Real-life operating tests of TiN-Cu coatings on replaceable WC-TiC-Co (79/15/6 wt.%) alloy hexagonal inserts used for cutting 40Kh steel revealed that applying the TiN-Cu coating extends the tool life of WC-TiC-Co inserts by about 2.5 times compared with uncoated tools. Cutting force measurements on TiN-Cu-coated inserts showed no vibration or noise during cutting, driven by a reduced friction coefficient and improved heat dissipation at the contact zone between the cutting edge and the workpiece, thereby lowering the temperature in that area. Full article

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16 pages, 12926 KB

Open AccessArticle

Friction and Wear Behavior of Carburized Steels Against Ceramic Balls Under Starved Lubrication

by Xu Liu, Linye Yu, Ming Zhong, Jin Qian, Jiapeng Dai and Yongan Min

Lubricants 2026, 14(4), 157; https://doi.org/10.3390/lubricants14040157 - 5 Apr 2026

Abstract

Starved lubrication poses a critical challenge to hybrid ceramic bearings operating under severe conditions. This study investigates the tribological behavior of carburized 20CrMo steel sliding against Al₂O₃ ceramic balls and GCr15 steel balls under dry sliding, with oil-lubricated tests as [...] Read more.

Starved lubrication poses a critical challenge to hybrid ceramic bearings operating under severe conditions. This study investigates the tribological behavior of carburized 20CrMo steel sliding against Al₂O₃ ceramic balls and GCr15 steel balls under dry sliding, with oil-lubricated tests as a reference. Under oil lubrication, the 20CrMo/Al₂O₃ pair exhibits superior wear resistance, attributed to the high hardness of the ceramic counterpart. Under dry sliding, however, this pair shows a slightly lower friction coefficient but a wear rate approximately three times that of the 20CrMo/GCr15 pair. This counterintuitive behavior stems from two mechanisms: lower contact stress and friction-induced work hardening in the GCr15 pair, which together suppress wear. Further analysis reveals that secondary carbides in the carburized layer detach under repeated high shear stress, acting as hard third-body abrasives and accelerating surface damage. These findings highlight that hybrid ceramic bearings are more susceptible to lubrication failure than all-steel bearings. Under heavy loads and poor lubrication, residual compressive stress plays a key role in governing the tribological behavior of carbides on carburized surfaces. Full article

(This article belongs to the Special Issue Advances in Tribology and Lubrication for Bearing Systems)

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27 pages, 5347 KB

Open AccessArticle

CFD-Based Analysis of Loading Performance and Hydrodynamic Effects in a Partial-Arc Aerostatic Radial Bearing

by Ruiran Ma, Jiashuo Zhang, Ming Feng, Zhixin Jia and Jin Wang

Lubricants 2026, 14(4), 156; https://doi.org/10.3390/lubricants14040156 - 5 Apr 2026

Abstract

With the widespread use of high-speed motorized spindles in precision machining, conventional contact loading methods are no longer adequate for stiffness loading tests under high-speed operating conditions. Non-contact loading technology based on a partial-arc aerostatic radial bearing offers an effective alternative. In this [...] Read more.

With the widespread use of high-speed motorized spindles in precision machining, conventional contact loading methods are no longer adequate for stiffness loading tests under high-speed operating conditions. Non-contact loading technology based on a partial-arc aerostatic radial bearing offers an effective alternative. In this study, a CFD-based hydrodynamic model was developed for the gas-film flow field in a partial-arc aerostatic radial bearing. The effects of bearing geometric parameters, such as chamber configuration, supply-orifice structure, and eccentricity, on loading characteristics were investigated. The influence of hydrodynamic effects under high-speed rotation on the loading force stability and stiffness-testing accuracy was analyzed, and an asymmetric shallow–deep composite chamber design was proposed to mitigate these effects. The results indicate that the partial-arc aerostatic radial bearing, designed based on both static characteristics and rotational performance analysis, can effectively suppress hydrodynamic effects and improve loading force stability and stiffness-testing accuracy. Full article

(This article belongs to the Special Issue Advances in Hydrodynamic Bearings)

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4 pages, 135 KB

Open AccessEditorial

New Horizons in Machine Learning Applications for Tribology

by Max Marian and Stephan Tremmel

Lubricants 2026, 14(4), 155; https://doi.org/10.3390/lubricants14040155 - 5 Apr 2026

Abstract

Tribology, the science of friction, wear, and lubrication, remains fundamental to modern engineering systems [...] Full article

(This article belongs to the Special Issue New Horizons in Machine Learning Applications for Tribology)

21 pages, 2452 KB

Open AccessArticle

A Detailed Multibody Simulation Model for Ball Bearings to Predict Friction and Electrical Capacitance

by Shashivar Syla, Kim Marius Brill, Stefan Paulus, Simon Graf and Oliver Koch

Lubricants 2026, 14(4), 154; https://doi.org/10.3390/lubricants14040154 - 3 Apr 2026

Abstract

A multibody simulation model for deep-groove ball bearings is presented. The model considers friction in both the raceway and cage contacts, resulting from radial and axial loads. The model is validated against experimental measurements for a 6319 bearing under oil-bath lubrication over a [...] Read more.

A multibody simulation model for deep-groove ball bearings is presented. The model considers friction in both the raceway and cage contacts, resulting from radial and axial loads. The model is validated against experimental measurements for a 6319 bearing under oil-bath lubrication over a speed range of 500–3000 min⁻¹ and two load ratios (

C / P = 10

and 6.5). Predicted friction torques show good agreement with measurements, with deviations between 5.5% and 22% at moderate speeds. In addition, electrical contact capacitances are calculated for a 6208 bearing and compared with an analytical approach, showing deviations in the range of 10–14%. Beyond friction prediction, the fully dynamic approach enables time-resolved analysis of roller kinematics and the identification of instability limits under axial excitation. The developed tool therefore enables reliable bearing loss prediction, supports efficiency-oriented drivetrain design, and provides a basis for electro-tribological and stability investigations. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings, 2nd Edition)

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23 pages, 9705 KB

Open AccessArticle

Wear Condition Assessment of Gear Transmission System Based on Wear Debris Boundary Energy

by Congrui Xu, Wei Cao, Yang Yan, Letian Ding, Yifan Wang, Rongrong Hao, Rui Su and Niraj Khadka

Lubricants 2026, 14(4), 153; https://doi.org/10.3390/lubricants14040153 - 1 Apr 2026

Abstract

The gear transmission system is the core component in industrial equipment, and its wear state directly affects the reliability and use life of equipment. The wear debris image contains important information on the mechanical wear state. By processing it and analyzing the characteristics [...] Read more.

The gear transmission system is the core component in industrial equipment, and its wear state directly affects the reliability and use life of equipment. The wear debris image contains important information on the mechanical wear state. By processing it and analyzing the characteristics and types of wear debris, the health status of mechanical equipment and components can be evaluated. However, wear debris images collected in real time are often affected by Gaussian noise. The improved K-SVD dictionary learning algorithm was used in this paper to remove Gaussian noise, using objective metrics to demonstrate the effectiveness of the improved K-SVD algorithm for wear debris images. Secondly, the improved marked watershed segmentation algorithm (B-FSL) was studied to segment the wear debris chains. After that, the boundary energy (BE) characteristics of the wear debris were extracted to warn about the severe wear state of equipment in advance, an EfficientNetB3 network based on transfer learning was constructed for the recognition and classification of the wear debris image, and the severity of the wear of the mechanical equipment was analyzed. Finally, an experiment was conducted to validate the above methods, proved that the BE characteristics of the wear debris can predict the failure of a planetary gearbox in advance, with the accuracy of the wear debris recognition and classification algorithm exceeding 98%. Full article

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22 pages, 8459 KB

Open AccessReview

Surface Modification of Equipment Under Extreme Conditions by Laser-Induced Thermal and Mechanical Effects

by Guangzhi He, Xiyan Wang, Yu Dai, Zhan Zhu, Xinhao Li, Donghua Jiang, Haoyuan Tan, Haitao Zhu and Zixiang Li

Lubricants 2026, 14(4), 152; https://doi.org/10.3390/lubricants14040152 - 1 Apr 2026

Abstract

Under extreme conditions in fields including aerospace exploration, deep earth excavation, and ocean engineering, mechanical components are subjected to severe environmental challenges, such as high temperature, heavy load, fatigue fracture and corrosion, which significantly limit their service life and operational reliability. Surface engineering [...] Read more.

Under extreme conditions in fields including aerospace exploration, deep earth excavation, and ocean engineering, mechanical components are subjected to severe environmental challenges, such as high temperature, heavy load, fatigue fracture and corrosion, which significantly limit their service life and operational reliability. Surface engineering has emerged as a critical strategy to address these problems by modifying surface characteristics while preserving basic properties of raw materials. Among various surface modification techniques, laser-based surface modification stands out due to its precise processing, high throughput, and outstanding surface performance. However, laser-based surface modification of metallic materials for industrial applications remains limited owing to inadequate systematic understanding regarding the fabrication mechanisms. Accordingly, a comprehensive and holistic review is essential to elucidate the effect of laser-based surface modification on process optimization, system development, microstructure evolution, and performance enhancement. This review systematically expounds two fundamental strategies in laser surface modification-based material modification (exemplified by laser cladding) and structural modification (exemplified by laser shock peening) in terms of mechanism, process, performance and application. In addition, the mechanism and potential of the synergistic integration of LC (laser cladding) and LSP (laser shock peening) are emphatically discussed. Finally, perspectives regarding process optimizations, material developments, and system improvements for laser surface engineering are presented. By establishing a clear “mechanism–process–performance–application” narrative, this review aims to provide both a scientific reference and a practical guideline for the severe demands of extreme operating conditions. Full article

(This article belongs to the Special Issue Laser-Assisted Surface Modification to Enhance Tribological Performance Under Extreme Conditions)

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13 pages, 1707 KB

Open AccessArticle

Numerical and Experimental Investigation of Fretting Wear in Connecting Rod Big-End Bearings of Nuclear Emergency Diesel Generators

by Shuai Zu, Pingsheng Hu, Xi Yang, Yang Li, Yinhui Che, Jianghong Zhang, Xiaohu Yang and Yi Cui

Lubricants 2026, 14(4), 151; https://doi.org/10.3390/lubricants14040151 - 31 Mar 2026

Abstract

The operational reliability of Emergency Diesel Generators (EDGs) is paramount for the safety of nuclear power plants. This study investigates the fretting wear mechanism on the non-working back-face of connecting rod big-end bearings—a critical failure mode that can lead to catastrophic engine damage. [...] Read more.

The operational reliability of Emergency Diesel Generators (EDGs) is paramount for the safety of nuclear power plants. This study investigates the fretting wear mechanism on the non-working back-face of connecting rod big-end bearings—a critical failure mode that can lead to catastrophic engine damage. A synergistic approach was employed, integrating theoretical pressure calculations, on-site strain measurement experiments, and high-fidelity non-linear finite element analysis (FEA). The results demonstrate that while the theoretical design back-face pressure ranges from 8.1 to 10.1 MPa, the actual pressure is highly sensitive to bolt preload. A 16.2% attenuation in preload (from 550 kN to 461 kN), common during maintenance cycles, causes the interfacial pressure to drop to 6.9 MPa, falling below the recommended safety threshold of 7 MPa required to inhibit fretting. Furthermore, comparative experiments reveal that used bearings exhibit significantly lower and less uniform radial pressure retention compared to new bearings, even when physical dimensions appear compliant. Dynamic FEA indicates that peak inertial loads induce an out-of-roundness (DOR) of 0.295 mm, triggering a transition from a “partial slip” to a “macro-slip” regime at the interface. The findings confirm that the coupling of preload attenuation and loss of bearing elasticity drives the fretting process, providing a theoretical basis for optimized maintenance and selective assembly strategies. Full article

(This article belongs to the Special Issue Lubrication and Tribology Challenges in Renewable Energy and High-Efficiency Power-Generation Systems)

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19 pages, 7968 KB

Open AccessArticle

Optimizing the Wide-Temperature Tribological Properties of HfO₂/WS₂ Coatings by Tuning Deposition Pressure

by Haibo Yu, Xiaopeng Zhang, Haichao Cai, Lulu Pei, Yujun Xue and Jing Liu

Lubricants 2026, 14(4), 150; https://doi.org/10.3390/lubricants14040150 - 31 Mar 2026

Abstract

To enhance the wear resistance and load-bearing capacity of WS₂ coatings, this paper employs unbalanced magnetron sputtering technology to fabricate HfO₂/WS₂ composite coatings by regulating the deposition pressure (0.6–1.4 Pa), leveraging the superior properties of HfO₂. The [...] Read more.

To enhance the wear resistance and load-bearing capacity of WS₂ coatings, this paper employs unbalanced magnetron sputtering technology to fabricate HfO₂/WS₂ composite coatings by regulating the deposition pressure (0.6–1.4 Pa), leveraging the superior properties of HfO₂. The microstructure, mechanical properties, and tribological behavior across a wide temperature range (room temperature to 450 °C) are systematically investigated. The results demonstrate that deposition pressure significantly modulates the coating structure and properties. At a deposition pressure of 0.6 Pa, a pronounced secondary bombardment effect leads to coarse surface particles, a thickness of only 1.525 μm, and a high hardness of 9.332 GPa, but inferior tribological performance with an average friction coefficient of 0.703. When the deposition pressure is increased to 1.4 Pa, the secondary bombardment effect weakens, resulting in an increased coating thickness of 2.125 μm, a decreased hardness of 3.88 GPa, and a significantly improved friction coefficient of 0.072. At an optimal deposition pressure of 1.0 Pa, the sputtered atoms possess moderate energy and optimal surface mobility, promoting the formation of a dense structure. The coating demonstrates a synergistic balance between mechanical load-bearing capability (hardness: 6.38 GPa) and a highly crystalline WS₂ structure, yielding superior frictional behavior characterized by a mean coefficient of friction (COF) of merely 0.062. High-temperature tribological evaluations indicate that the COF displays a non-monotonic trend, declining at first before ascending as the temperature elevates. A minimum value of 0.015 is reached at 300 °C, corresponding to a wear rate of 1.127 × 10⁻⁸ mm³·N⁻¹·m⁻¹. At 450 °C, partial oxidation of WS₂ to WO₃ causes the friction coefficient to rise to 0.045, accompanied by fluctuations. Microstructural analysis confirms that HfO₂ doping effectively suppresses the oxidation of WS₂ at elevated temperatures and promotes the preferred growth orientation of the WS₂(002) plane, thereby synergistically optimizing the wide-temperature-range lubrication performance of the coating. This study provides a novel technical approach for the design of lubricating coatings intended for high-temperature and harsh operating conditions, such as those encountered in aero-engine bearings. Full article

(This article belongs to the Special Issue Advances in Thin Film Tribology)

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15 pages, 5628 KB

Open AccessArticle

Fretting-Corrosion Behavior of Stellite 6 Overlay Welded on 304 Stainless Steel in Simulated PWR Water Environment

by Yuanbin Gui, Chengtao Li, Zhaoguang Zhu, Sunwu Xu, Bin Yang, Qianwu Li, Jing Wan and Shugang Zhang

Lubricants 2026, 14(4), 149; https://doi.org/10.3390/lubricants14040149 - 31 Mar 2026

Abstract

The fretting-corrosion behavior of a Stellite 6 cobalt-based overlay welded to 304 stainless steel was investigated in simulated high-temperature, high-pressure PWR water. Three material pairings were examined: Stellite 6/Stellite 6 (C-C), Stellite 6/304 stainless steel (C-S), and 304 stainless steel/304 stainless steel (S-S). [...] Read more.

The fretting-corrosion behavior of a Stellite 6 cobalt-based overlay welded to 304 stainless steel was investigated in simulated high-temperature, high-pressure PWR water. Three material pairings were examined: Stellite 6/Stellite 6 (C-C), Stellite 6/304 stainless steel (C-S), and 304 stainless steel/304 stainless steel (S-S). Wear behavior was evaluated in terms of mass loss, surface morphology, surface chemistry, friction evolution, and subsurface deformation. The results show that material pairing strongly affects friction stability and damage evolution during fretting corrosion. The C-C contact exhibited a relatively stable coefficient of friction and continuous wear morphology, with damage dominated by plastic deformation. In contrast, the C-S and S-S contacts exhibited stronger wear–corrosion interaction, characterized by debris accumulation, oxide film instability, and fluctuating friction behavior. Despite the same oxide species being observed in different contact pairs, their distribution and stability varied greatly, which resulted in different modes of damage. EBSD analysis showed that fretting energy in the C-C contact was mainly accommodated by plastic strain in the near-surface region, whereas deformation in the C-S and S-S contacts was more localized and discontinuous. These results indicate that oxide film stability and subsurface strain distribution jointly control friction behavior and fretting-corrosion damage under different material pairings. Full article

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19 pages, 13697 KB

Open AccessArticle

Effect of Cr Doping Content on the Mechanical and Tribological Properties of Cr-C/DLC Films on ACM Rubber Surfaces

by Kanghai Chen, Nini Zhen, Huatang Cao, Qiaoyuan Deng and Feng Wen

Lubricants 2026, 14(4), 148; https://doi.org/10.3390/lubricants14040148 - 31 Mar 2026

Abstract

Recently, diamond-like carbon (DLC) films have been considered for enhancing the wear resistance of rubber because rubber exhibits a high coefficient of friction and is prone to wearing out. However, the significant difference in thermal expansion coefficients between DLC films and rubber often [...] Read more.

Recently, diamond-like carbon (DLC) films have been considered for enhancing the wear resistance of rubber because rubber exhibits a high coefficient of friction and is prone to wearing out. However, the significant difference in thermal expansion coefficients between DLC films and rubber often leads to high residual stresses and poor interfacial adhesion, which limits their application in dynamic seals. In this study, Cr-C/DLC composite films were prepared using magnetron sputtering, and the effects of varying Cr contents (0.8 at.%, 1.4 at.%, 4.3 at.%, and 7.0 at.%) on interfacial adhesion and tribological properties were investigated. Scanning electron microscopy (SEM) analysis revealed no distinct demarcation lines in the composite films, indicating strong adhesion to the substrate. X-ray photoelectron spectroscopy (XPS) analysis revealed that chromium doping promoted the conversion of sp³ bonds to sp² bonds. Adhesion and tribology tests revealed that introducing a Cr-C layer with higher Cr content within the range of 0.8 at.% to 7.0 at.% enhanced the film’s adhesion, reducing the CoF value of the composite film to 0.13–0.14. Specifically, the RF80 sample (4.3 at.% Cr) exhibited excellent interfacial adhesion and optimal tribological performance, with a CoF value reduced to 0.13 and wear rate of 3.1 × 10⁻⁴ mm³/(Nm). In summary, modulating the Cr doping content can significantly enhance the interfacial adhesion strength and tribological properties of Cr-C/DLC composite films on rubber surfaces, providing an effective solution for optimizing rubber seals. Full article

(This article belongs to the Special Issue Advanced Protective Composite Coatings and Films: Tribological Mechanisms and Applications)

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11 pages, 2133 KB

Open AccessArticle

Atomic-Scale Insights into the Dynamic Friction Regulation Mechanisms of Nanolubricant Molecules at the Fe/PTFE Interface

by Fan Xue, Tianqiang Yin, Guoqing Wang, Jingfu Song, Qingjun Ding, Dae-Eun Kim and Gai Zhao

Lubricants 2026, 14(4), 147; https://doi.org/10.3390/lubricants14040147 - 31 Mar 2026

Abstract

Surface and interface science play an important role in the tribological properties of materials. Recently, research in this field has extended from the macroscopic scale to the molecular level to elucidate energy dissipation and structural evolution mechanisms at sliding interfaces. In this work, [...] Read more.

Surface and interface science play an important role in the tribological properties of materials. Recently, research in this field has extended from the macroscopic scale to the molecular level to elucidate energy dissipation and structural evolution mechanisms at sliding interfaces. In this work, we propose a nanolubricant strategy based on carbon nanocages (CNCs). Three types of lubricating molecules—oleylamine (amine), oleic acid (carboxyl), and stearyl alcohol (hydroxyl)—were encapsulated into a polytetrafluoroethylene (PTFE) matrix to construct a composite tribological interface model. Molecular dynamics simulations were employed to investigate the interfacial enrichment, diffusion, and interaction mechanisms of these molecules with PTFE chains and the Fe counterface. Particular emphasis was placed on how different functional groups regulate energy transfer and dissipation pathways. This study deepens the molecular–level understanding of structure–lubrication relationships and provides theoretical guidance for designing high–performance polymer–based tribological materials. Full article

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19 pages, 9863 KB

Open AccessArticle

Analysis of Slope Braking Adaptability of Copper-Based Powder Metallurgy Brake Pads for High-Speed Trains Based on Full-Scale Bench Tests

by Xueqian Geng

Lubricants 2026, 14(4), 146; https://doi.org/10.3390/lubricants14040146 - 31 Mar 2026

Abstract

With the opening of complex service routes, the importance of the service performance of brake pads under long slope braking conditions is increasing. It is necessary to analyze the slope braking adaptability of current brake pad products. This work takes the copper-based powder [...] Read more.

With the opening of complex service routes, the importance of the service performance of brake pads under long slope braking conditions is increasing. It is necessary to analyze the slope braking adaptability of current brake pad products. This work takes the copper-based powder metallurgy brake pads of a certain in-service high-speed train as the research object and conducts friction and wear behavior tests of the brake pads based on a full-scale brake test bench. Through microscopic observation and damage analysis, the differences in friction and wear behavior of the brake pads under stop braking and slope braking conditions are compared, revealing the wear mechanism and damage evolution characteristics of the brake pads. The results show that under the impact of high speed, high braking force, and severe thermal load in the stop braking conditions, the uneven wear of brake pads is high, and the eccentric wear of friction blocks is affected by both the friction radius and friction direction. The friction surface has a large number and size of damages, and the stability of the friction interface is poor. The brake pad exhibits a composite wear mechanism dominated by abrasive wear and brittle fracture induced exfoliation. In the slope braking condition, under the action of low speed, low braking force, and long-term stable thermal load, the uneven wear of the brake pads is relatively low, the surface damage size is small, and the friction block only has eccentric wear along the friction direction. The brake pad mainly initiates cracks along the interface of the components, which propagate parallel to the friction surface, exhibiting a progressive delamination and flaking exfoliation mechanism with a low wear rate. Although the friction interface of the brake pad is relatively stable under slope braking conditions, the cumulative delamination wear of the brake pads under long-term braking action needs further attention. Full article

(This article belongs to the Special Issue Thermomechanical Tribological Behaviors and Damage Failure in Engineering Applications (2nd Edition))

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18 pages, 2139 KB

Open AccessArticle

Influence of the Cage on the Friction Torque in Miniature Angular Contact Ball Bearings

by Alina Corina Dumitrașcu, Denis Cojocaru, Vlad Cârlescu, Andrei Zaharia and Dumitru Olaru

Lubricants 2026, 14(4), 145; https://doi.org/10.3390/lubricants14040145 - 31 Mar 2026

Abstract

In this paper, the authors have analytically and experimentally investigated the friction torque in an angular contact ball bearing (ACBB) considering the following configurations: (i) a modified ball bearing with three equidistantly positioned balls without a cage and (ii) three modified ball bearings [...] Read more.

In this paper, the authors have analytically and experimentally investigated the friction torque in an angular contact ball bearing (ACBB) considering the following configurations: (i) a modified ball bearing with three equidistantly positioned balls without a cage and (ii) three modified ball bearings having four, six and eight balls with a phenolic cage. The experimental tests were realised at a low axial load and a rotational speed between 100 and 500 rpm under lubricated conditions. The test results for the ACBB with three balls without a cage showed that the friction torque is generated only by the rolling contacts between the balls and the two raceways in lubricated conditions. Considering the low axial load, the influence of the hydrodynamic rolling resistance was the dominant source of the frictional torque. The cage presence added supplementary friction, causing the friction torque to increase up to 60–65% compared to the cage-less configuration. Also, an additional increase in the frictional torque by 35–40% was observed for every two additional balls. The friction torque component that is generated by the cage presence does not depend on the number of balls added but rather on the rotational speed. All the tests were performed using the spin-down methodology, and the resulting friction torques (T_exp) were determined by integrating the dynamic equation during the deceleration process using Python-based software (Python version 3.10). The input and output parameters are presented for each test. Logarithmic diagrams revealing the dependence between the experimental friction torque and angular speed were obtained and fitted, and the relations have been determined for all tests. The analytical results of the friction torque were obtained based on Houpert’s model for all modified ball bearing configurations. Full article

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23 pages, 8751 KB

Open AccessArticle

Design of Axial Profiling and Investigation of the Influence of Pocket Position on Lubricant Flow in Planetary Journal Bearings in Applications with Low Sliding Speeds and High Loads

by Sören Henniger, Jan Zwinge, Gino Grossi, Thomas Hagemann and Hubert Schwarze

Lubricants 2026, 14(4), 144; https://doi.org/10.3390/lubricants14040144 - 31 Mar 2026

Abstract

The application of plain bearings has become very famous in planetary gear stages in recent years. To improve load-carrying capacity, this study investigates a design method for axial profiling in which a sixth-order polynomial is iteratively derived from the curve of local minimum [...] Read more.

The application of plain bearings has become very famous in planetary gear stages in recent years. To improve load-carrying capacity, this study investigates a design method for axial profiling in which a sixth-order polynomial is iteratively derived from the curve of local minimum film thickness for each axial grid position. Two load cases with specific bearing loads of 12.0 MPa and 6.0 MPa at 0.5 m/s are considered for profile design. Calculation results and computational effort of strategies assuming rigid or elastic geometries during the optimization are compared. Results indicate that the consideration of deformation is already necessary in the design phase and a maximization of minimum film thickness leads to much higher load-carrying capacity than the minimization of the maximum film pressure. Furthermore, the impact of the lube oil pocket position on oil flow rate is experimentally and theoretically investigated to identify the optimization potential of this parameter. Results show that the oil flow varies by the factor of three if the lube oil pocket is shifted incrementally over an angular span of 180° outside the load zone. The results and possible extensions are critically discussed under the consideration of practically relevant restrictions in mechanically highly loaded planetary gearboxes. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings, 2nd Edition)

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13 pages, 1408 KB

Open AccessArticle

Effects of Different Particles on the High-Temperature Oxidative Degradation Behavior of Aviation Lubricating Oil

by Shizhao Yang, Jiaming Guo, Jingpei Cao, Jianqiang Hu, Xin Xu, Liping Tong, Jingping Zhao, Jun Ma and Ping Qi

Lubricants 2026, 14(4), 143; https://doi.org/10.3390/lubricants14040143 - 29 Mar 2026

Abstract

The effects of dust, copper particles, and iron particles on the high-temperature oxidative degradation behavior of aviation lubricating oil were systematically examined, and the high-temperature catalytic oxidation effects of single-particle and mixed-particle systems on the lubricating oil were further analyzed, respectively. Gas chromatography/mass [...] Read more.

The effects of dust, copper particles, and iron particles on the high-temperature oxidative degradation behavior of aviation lubricating oil were systematically examined, and the high-temperature catalytic oxidation effects of single-particle and mixed-particle systems on the lubricating oil were further analyzed, respectively. Gas chromatography/mass spectrometry analysis results indicated that significant differences exist in the catalytic oxidation activity of particles toward lubricating oils, with the activity ranking in the descending order of copper particles > iron particles > dust. Notably, following oxidation by both metal and dust particles, the acid value, particle size, and viscosity of the oil sample exhibit a significant synergistic catalytic effect, even exceeding those of the oil sample oxidized by the same amount of metal particles. Specifically, relative to the pristine oil, the oil oxidized with 5 mg of copper particles and 5 mg of dust exhibits respective increases of 213.3%, 316.11%, and 661.43% in the aforementioned properties. This variation is attributed to the physical adsorption and chemical reactions between dust and antioxidants during oxidation, which deplete antioxidants and thereby exacerbate oil oxidation. Furthermore, this study further elucidates the potential synergistic oxidation mechanism induced by metal particles and dust particles. Full article

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19 pages, 8878 KB

Open AccessArticle

Comparative Performance of Ni- and Fe-Based Mixed Alloy Brazed Coatings via Laser Remelting

by Marco Brand, Mareen Goßling, Ion-Dragoş Uțu and Gabriela Mărginean

Lubricants 2026, 14(4), 142; https://doi.org/10.3390/lubricants14040142 - 29 Mar 2026

Abstract

Traditionally, repairing coated substrates requires completely removing damaged, wear-resistant layers before recoating. This process leads to high costs, extended downtime, and material waste. Flexible brazing tapes, which are composed of alloy powder and an organic binder, offer an alternative to full coating removal [...] Read more.

Traditionally, repairing coated substrates requires completely removing damaged, wear-resistant layers before recoating. This process leads to high costs, extended downtime, and material waste. Flexible brazing tapes, which are composed of alloy powder and an organic binder, offer an alternative to full coating removal for targeted repairs. Despite this, the process of vacuum brazing these tapes may lead to the formation of defects, including pores caused by trapped gases or residual binder, which compromise coating durability and corrosion resistance. This study focuses on the utilization of laser remelting as a method for post-processing nickel- and iron-based mixed alloy brazing tapes, with the aim of improving the integrity of the coating. Surface quality was assessed via microscopy and microhardness testing by systematically varying laser power, scanning speed, and hatch distance. Among the parameters studied, the most suitable laser parameter combination was found to be 350 W laser power, 250 mm/s scanning speed, and a hatch distance of 0.02 mm. These parameters yielded crack- and pore-free coatings with a remelting depth of 160.3 ± 17.2 µm and a microhardness of 701 ± 23 HV1, which is an 85% increase over as-brazed samples. Wear testing revealed a reduced coefficient of friction, and electrochemical corrosion tests showed lower corrosion current density and enhanced repassivation behavior in remelted coatings. These improvements demonstrate that laser remelting significantly enhances the microstructure, hardness, wear resistance, and corrosion performance of brazed coatings, providing an effective method for localized repair while minimizing material consumption and processing duration. Full article

(This article belongs to the Special Issue Analysis, Evaluation and Diagnosis of Tribological Phenomena in Machining Processes)

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44 pages, 11387 KB

Open AccessArticle

Integrated Theoretical Modeling and MASTA-Based Parametric Simulation for Contact Mechanics, Wear Behavior, of Critical Bearings in RV Reducers

by Weichen Kong, Xuan Li, Gaocheng Qian and Jiaqing Huang

Lubricants 2026, 14(4), 141; https://doi.org/10.3390/lubricants14040141 - 27 Mar 2026

Abstract

RV reducers are vital components in industrial robots and precision equipment, where the fatigue life of the crank arm and support bearings critically influences the overall system longevity. This study presents a comprehensive performance evaluation, with a specific focus on contact mechanics and [...] Read more.

RV reducers are vital components in industrial robots and precision equipment, where the fatigue life of the crank arm and support bearings critically influences the overall system longevity. This study presents a comprehensive performance evaluation, with a specific focus on contact mechanics and wear analysis of these critical bearings. A theoretical mathematical model for force analysis is established based on static mechanics, which is further extended to incorporate wear depth prediction based on contact pressure and sliding velocity. To validate this model and investigate bearing behavior in detail, a high-fidelity parametric simulation model is developed using MASTA software. The simulation results, encompassing contact stress, shear stress, and wear patterns, demonstrate good correlation with the predictions from the theoretical mathematical model, effectively verifying its accuracy for performance and life assessment. The systematic analysis confirms that both the investigated tapered roller and needle roller bearings meet the design requirements. This integrated approach of theoretical modeling, which includes wear analysis, and software simulation provides a reliable methodology for assessing bearing performance and fatigue life, offering significant value for the design optimization and reliability enhancement of RV reducers. Full article

(This article belongs to the Special Issue Tribology of Cycloidal Reducers: Enhancing Efficiency, Durability and Reliability through Experimental and Numerical Methods)

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